The diagnosis of prostate cancer is still a difficult proposition. Diagnostic imaging such as MRI and ultrasound do not reliably detect tumors, while more advanced methods such as SPEC are still under development and in all likelihood will be costly. With more than 200,000 men diagnosed with prostate cancer and about 30,000 deaths per year in the US, a need for an inexpensive screening technology is felt. We have been able to demonstrate experimentally on a small number of patients that prostate cancer is associated with an increased resistance compared to surrounding tissue. This has also been observed by other researchers. In our preliminary study, no effort was made to use the information in the reactance of the prostate. We hypothesize that the dispersion behavior of prostate tissues may hold additional information that may be of use in differentiating between various types of abnormalities in the prostate and may assist physicians in deciding on a course of action. This is also of interest, since at times there is still some debate on what is the best course of action. We propose to combine two inexpensive imaging modalities to create a reliable tool to screen for prostate cancer. Impedance measurements performed through the rectal wall will be used to detect cancerous nodules. The ultrasound imager to which our system will be coupled will serve to produce anatomic information which in turn will be used to reconstruct volumetric impedance maps in real time. Imaging information from both sources will be presented independently and in co-registered overlays. The impedance sensors and the intrarectal ultrasound scanhead will be physically coupled and their spatial relationship calibrated so that information from the two modalities will be spatially co-registered. We propose to design a modified ultrasound applicator which will incorporate an array of intracavitary electrodes. These electrodes, coupled with an external electrode applied onto the patient's abdomen will produce switchable current patterns which will flow through the prostate and as a result allow the instrument to sense variations in impedance in that organ. In the proposed 3 years of the project, we intend to build our custom applicator, test it on phantoms and patients. We also will develop new electronics and reconstruction techniques applicable to this configuration. This project capitalizes on our group's extensive experience in impedance imaging.